A camera module mounted on a portable phone or the like has a structure including (i) a solid-state image sensor, (ii) a glass substrate, (iii) a wired board with terminals, (iv) a lens, and (v) a holder (lens holder) for holding the lens. The solid-state image sensor is, for example, CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) image sensor.
Recently, the solid-state image sensor has been further miniaturized. Thus, if there is a foreign material present in a light receiving portion of the solid-state image sensor, in an optical path in which light to enter the solid-state image sensor travels on the glass substrate, or in the like position, shadow of the foreign material would be possibly captured on a screen on which a captured image is displayed. On the screen, the shadow of the foreign material appears as a black spot, or stain, thereby causing defection in the image captured by the camera module. In the following, such a foreign material is referred to as “dust”. Furthermore, if the dust is of such a minute size that it has a size of 30 μm or less, or about 20 μm, the dust not only causes the shadow or black spot on the screen, but also is difficult to remove from the camera module because the dust can enter gaps formed in non-flat portions in a micro lens arrays.
Here, the dust contaminating the inside the camera module can be classified generally into two types: process-origin dust; and material-origin dust.
Examples of the process-origin dust encompass ones generated by wearing of devices used in a manufacturing process of the camera module, ones (hair and the like) derived from a body of a worker in the manufacturing process, and the like dust. The material-origin dust is relatively large (to be visible by human eyes) and is easy to find and remove by inspections or the like.
Examples of the material-origin dust encompass (i) ones carried by components of the camera module when the components are shipped in, (ii) exfoliation (such as filler) fallen off from a molded resin or an adhesive agent, (iii) dust worn off from an auto focusing or zooming operating mechanism or component during its operation, and (iv) the like. The material origin dust often very small in size, because it would be minute resin pieces, a fallen-off filler, or the like.
If dust of a visible size is present on the glass substrate, it is easy to remove the dust from the glass substrate. However, if minute dust is attached to a wall surface of the lens holder, a surface of the wiring board, etc. other than the light receiving portion (micro lens array) of the solid-state image sensor, it is difficult to detect the dust by inspection or the like. Failure of detecting the dust would lead to shipping out a defective camera module having a risk of causing defective image capturing. If the dust is moved to the light receiving portion (micro lens array) of the solid-state image sensor by vibration and/or impact during transportation or delivery, the camera module is impaired at a dealer or a user.
The glass substrate is not only a component having optical functions such as a function as an optical filter as described above, but also a component for preventing dust from contaminating the light receiving portion (micro lens array) of the solid-state image sensor, the wall surface of the lens holder, the surface of the wired board, etc.
Patent Literatures 1 to 3 discloses techniques as to assembling structures that such a glass substrate has for the purpose of preventing the dust contamination.
The object of the technique disclosed in Patent Literature 1 is to accurately determine a distance between an optical system of an image capturing device lb and an image capturing surface 211, and a tilting of the optical system with respect to the image capturing surface 211. In order to attain the object, the Patent Literature 1 discloses the following technical feature. From above an electrically conductive adhesive agent (such as silver paste) applied on an electrode on a steric circuit substrate 3, a glass substrate 22 is pressed against the steric circuit substrate 3 via a ball bump 221b. By deforming the ball bump 221b by a force of the pressing, the glass substrate 22 is adhered to a mounding reference surface 351 in such a state that the glass substrate 22 is abutted against the mounting reference surface 351, which is a top edge of a protrusion section 35b (see FIG. 25).
The technique disclosed in Patent Literature 1, an image capturing device 21 is mounted on the steric circuit substrate 3 with the highly-flat glass substrate 22 imposed therebetween. This makes it possible to mount the image capturing device 21 on the steric circuit substrate 3 easily and accurately. Furthermore, the glass substrate 22 has a thermal expansion coefficient (about 8×10−6/° C.) smaller than that (about 25×10−6/° C.) of a resin substrate. This reduces a heat stress applied on a position (connection portion) at which the image capturing device 21 and the glass substrate 22 are connected with each other, thereby giving a better connection reliability to the image capturing device 21.
Patent Literature 2 discloses the following technical feature. On an upper surface of a ring-shaped connection section 34 of a frame-shaped member 30, a thermally-curing adhesive agent 40 (illustrated by hatching with oblique lines) is applied. The adhesive agent 40 is applied selectively on a region other than a groove region B, which is that part of the upper surface of the ring-shaped connection section in which grooves 36 are provided (see FIG. 26).
Patent Literature 3 discloses the following technical feature. A camera module has a pedestal portion having an abutting section positioned apart from side walls, and connection sections positioned at corners between adjacent side walls, and a bank section. The abutting section is not for bonding with a glass cover but is for abutting against the glass cover so as to determine position of the glass cover with respect to a mounding surface of the pedestal portion, and to determine a tilting angle of the glass cover. The abutting section and the bank section further have a function of banking up an adhesive agent to prevent the adhesive agent from flooding into an image capturing region. By this, a good image capturing quality is ensured meanwhile a wide-spreading of a connection region is prevented. Like the abutting section, the bank section also abuts against the glass cover in bonding the pedestal portion and the glass cover with each other. Meanwhile, the connection section is lower than the abutting section, so that the connection section will not touch the glass cover in bonding the pedestal portion and the glass cover with each other. Thus, the bonding the pedestal portion and the glass cover with each other crease a gap between the connection section and the glass cover. The bonding between the connection section and the glass cover is carried out in the gap.